Sealed food container and method of ensuring delivery of the container in a heated state

ABSTRACT

A food container for carrying a heated food product that is provided with a seal which connects the lid of the container to the body portion thereof and visually indicates that the food container has been maintained in a heated condition.

This patent application is a continuation-in-part of my prior U.S.patent application Ser. No. 09/531,260 filed on Mar. 17, 2000, now U.S.Pat. No. 6,169,770.

FIELD OF THE INVENTION

This invention relates generally to containers for carrying a heatedfood product and more particularly concerns a sealed food containerprovided by a seal that is tamper proof and visually indicates that thecontainer is in a heated state and also concerns a method of visuallyensuring that the food container when transported from the place whereit is prepared to the customer's door is in a heated condition.

BACKGROUND AND SUMMARY

My U.S. Pat. No. 6,018,143, entitled Heat Thermal Bag, issued on Jan.25, 2000 discloses a portable heating container or thermal bag forcarrying a food product such as a pizza. The thermal bag has top andbottom panels and is closed at the rear end and at the sides, but has anopening at the front for the insertion and removal of the food product.The bag is insulated and has a built-in heating device with a thermostatto maintain the bag at a desired temperature. The heating device isintended to be plugged into the cigarette lighter of the deliveryvehicle so that the bag remains heated up to the point of actualdelivery to the customer. Thus, the pizza or other food product in thebag will remain oven hot no matter what weather conditions, trafficconditions or delivery distance prevail. A thermofuse is employed toprevent overheating as might occur as a result of failure of thethermostat.

When properly used, the thermal bag described above will maintain aconstant temperature of 160 degrees Fahrenheit to 175 degrees Fahrenheitso that the food product is maintained at a desired temperature whilebeing transported from one location to another. If not properly used,however, the temperature of the thermal bag can drop resulting in thefood product not being maintained at the desired temperature whendelivered to the customer. This, of course, affects the quality of thefood product and often creates an unhappy customer who may decide to nolonger make any additional purchases from the party preparing andselling the food product.

Accordingly, one object of the present invention is to provide a new andimproved seal for a food container that renders the food containertamper-proof and serves to visually indicate to a customer that the foodcontainer has been maintained in a heated state.

Another object of the present invention is to provide a new and improvedportable food container for carrying a heated food product for deliveryto a customer and in which the container is provided with a seal thatwill require the container to be maintained at a desired temperature.

A further object of the present invention is to provide a new andimproved portable food container for heated food products that isprovided with a seal which prevents tampering with the contents of thecontainer and also serves to verify visually that the container is at orabove a desired temperature.

A still further object of the present invention is to provide a new andimproved method of transporting a heated food product in a portable foodcontainer from the place where the food has been prepared to thecustomer's door while maintaining the food container at a constanttemperature and ensuring visually that the contents of the foodcontainer is at or above a desired temperature when given to thecustomer.

A still further object of the present invention is to provide a new andimproved method of ensuring that a portable food container carrying aheated food product is not tampered with and is at a desired temperatureafter being transported by a motor vehicle from the store where it wasprepared to a customer's door.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description of theinvention when taken with the drawings in which:

FIG. 1 is a perspective view of a front compartment of a motor vehicleprovided with a portable heated container having a two removable foodcontainers therein in accordance with the present invention with theheated container situated along side of a vehicle driver and beingtransported by a vehicle driver for delivery to a customer of the heatedfood products within the food containers;

FIG. 2 is a perspective view of the portable heated container seen inFIG. 1 with its flap opened to reveal the two food containers;

FIG. 3 is a perspective view of one of the food containers seen in FIG.2 having its lid in the open position to reveal the heated food product;

FIG. 4 is a perspective view of the food container seen in FIG. 3 havingits lid closed and joined to the body portion of the food container by aseal containing a heat sensitive coating on an indicia that serves tovisually indicate whether the food container is at a desiredtemperature;

FIG. 5 is an enlarged view of the seal applied to the food containerseen in FIG. 4 showing the condition of the heat sensitive coating whenit is at a temperature below a predetermined temperature;

FIG. 6 is a view of the seal seen in FIG. 5 showing the condition of theheat sensitive coating when it is at or above a predeterminedtemperature;

FIG. 7 is an enlarged sectional view of the seal taken on line 7—7 ofFIG. 5;

FIG. 8 is an enlarged sectional view of the seal taken on line 8—8 ofFIG. 6;

FIG. 9 is a view of a modified version of the seal seen in FIGS. 4-8;

FIG. 10 is a further modified version of the seal seen in FIGS. 4-9; and

FIG. 11 is a sectional view taken on line 11—11 of the seal seen in FIG.10.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more particularly to FIGS. 1 and 2thereof, the front compartment of a motor vehicle 10, such as a van, isshown with a vehicle operator 12 seated behind the steering wheel 14 ofthe vehicle 10. In this case, the vehicle operator 12 serves as adelivery person of heated food products located within a portablethermal bag or heated container 16 that is shown positioned along sideof the vehicle operator 12 and resting on the floor portion 18 of thevehicle 10. The heated container 16 includes an electric lead 20attached to the rear of the heated container 16 that terminates with aquick release connector 22. The connector 22 is coupled to a matingconnector 24 of a power cord 26 which has a plug 28 on the other endthat is plugged into an electric outlet or receptacle such as thecigarette lighter 30 of the vehicle 10.

The heated container 16, seen in FIGS. 1 and 2, has a top panel 32 and asimilar bottom panel 33 and includes side panels 34 and 36 that closethe sides of the heated container 16. The heated container 16 is closedat the rear by a rear panel 38 and has an opening at the front thatleads to a cavity 40 defined by the panels 32-38. A closure member orflap 42 is integrally formed with the bottom panel 33. As should beapparent, the flap 42 is foldable up over the top panel 32 to sealinglyclose the opening leading to the cavity 40. The flap 42 is held closedby cooperating strips of hook and loop fasteners 44 and 46, such asVelcro, on the inner surface of the flap 42 and on the outer surface ofthe top panel 32, respectively.

The panels 32-38 of the heated container 16 are preferably rectangular,as shown with the top and bottom panels 32 and 33 and the rear panel 38being formed from one continuous multi-layer length of flexiblematerial. Each of the panels 32-38 and the flap 42 are formed with anembedded flexible layer of insulation (not shown) for heat retention. Inaddition, the top and bottom panels 32 and 33 have a layer of resinousplastic material (not shown), such as polyurethane form, embeddedtherein with each layer of plastic material having an electricresistance wire (not shown) arranged in a serpentine manner and securedthereto by an adhesive. The resistance wire in each panel 32 and 33serves as a heating element to keep the contents of the heated container16 at a constant temperature range of 160 degrees Fahrenheit to 175degrees Fahrenheit through a thermostat (not shown) located in the toppanel 32. The resistance wires in the panels 32 and 33 are connected tothe lead wire 20 attached to the rear of the heated container 16. A moredetailed description of the construction of the heated container 16 canbe found in my aforementioned U.S. Pat. No. 6,018,143 and reference ismade thereto for this purpose.

As seen in FIG. 2, two identical rectangular food containers 48, each inthe form of a box, are located within the cavity 40 of the heatedcontainer 16. As seen in FIGS. 3 and 4, each of the food containers 48includes a rectangular body portion 50 provided with a hinged lid 52,both of which are made of cardboard. The body portion 50 of the foodcontainer 48 includes a rectangular base section 53 integrally formedwith upstanding front and rear walls 54 and 56, respectively, and a pairof laterally spaced upstanding side walls 58 and 60. The lid 52 has arectangular top section 62 integrally formed with a pair of downwarddepending laterally spaced side walls 64 and 66 and a front wall 68. Acentrally located tab 70 is cut out of the front wall 68 and is used tofacilitate opening and closing of the lid 52. In addition, the lid 52 ishingedly connected to the rear wall 56 of the body portion 50 of thefood container 48 at a score line 72 extending the length of the rearwall 56. Accordingly, the lid 52 is adapted to be folded downwardlyabout the score line 72 to a closed position wherein the side walls 64and 66 and the front wall 68 of the lid 52 are located, as seen in FIG.4, within the confines of the body portion 50 adjacent the side walls 58and 60 and front wall 54. Food containers of this type are typicallyused for accommodating a heated pizza 74 as shown in FIG. 3. Once thelid 52 is closed, the hot pizza 74 is located in a closed rectangularchamber 76, the inner air of which becomes heated due to the heat lossof the pizza 74. The insulating properties of the cardboard, althoughlimited to some extent, serve to prevent the heat in the chamber 76 frombeing rapidly dissipated. Various pizza companies such as Pizza Hut,Little Caesars, and Domino's as well as various “Mom and Pop” storesutilized a food containers of the above-described type for holding aheated pizza.

Although food containers of the above-described type provide some heatretention for a food product such as the heated pizza 74, there are somepizza stores that prolong the heat retention by placing the foodcontainer 48 under a heat lamp prior to pick-up by a customer. However,it has been found that in cases where the food container must betransported to a customer's door, the cardboard of the food container 48has insufficient insulating properties to be capable of maintaining thefood product at a desired temperature. For this reason, it is becomingquite common for the food containers to be placed in the portable heatedcontainer 16 as seen in FIG. 2. However, as alluded to hereinbefore, ifthe heating container 16 is not used properly, the temperature withinthe cavity 40 can drop. As a result, the food container 48 and, as aconsequence the food product, may not be maintained at a desiredtemperature. In an effort to prevent this from occurring, the foodcontainer 48 is provided with a seal 78 having a substrate 80 in theform of a rectangular sheet preferably made of sixty pound whitesemi-gloss paper. As seen in FIGS. 5 and 6, the front side of thesubstrate 80 has certain words printed thereon regarding temperature andindicating that the pizza 74 should only be accepted if the words “It'sHOT” are visible. In addition, on the backside of the substrate 80,pressure sensitive adhesive is coated thereon, as seen in FIGS. 7 and 8,that serves to securely join or connect the front wall 54 of the bodyportion 50 of the food container 48 to the top section 62 of the lid 52.The substrate 80 of the seal 78 is also provided with a plurality ofstraight line perforations 84 which, when the seal 78 is applied on thefood container 48, are aligned with the intersection of the front wall54 with the plane of the top section 62 as seen in FIG. 4. Moreover, thesubstrate 80 of seal 78 is provided with a localized circular heatsensitive coating 86 over the words “It's HOT”. This heat sensitivecoating 86 is opaque, as seen in FIGS. 5 and 7, when it is below apredetermined temperature and the heat sensitive coating 86 is clear, asseen in FIGS. 6 and 8, to reveal the words “It's HOT” when it is at orabove a predetermined temperature. The heat sensitive coating 86 is madeof a reversible thermochromic composition which, upon being heated to apredetermined temperature, changes from the opaque colored state ofFIGS. 5 and 7 to the colorless state of FIGS. 6 and 8 to expose thewords “It's HOT” as seen in FIG. 6.

The heat sensitive coating 86 on the seal 78 is available from a companyknown as Promo Edge, which is a division of Menasha Corporation, and islocated at 950 Breezewood Lane, P.O. Box 4276, Neenah, Wis. 54957-0427.Promo Edge identifies the heat sensitive coating 86 as a “ClearingTemperature Sensitive Ink”. The particular “Clearing TemperatureSensitive Ink” used in making the heat sensitive coating 86 isidentified by Promo Edge as Type 45 ink. By experimentation, I foundthat the Type 45 ink provides a temperature range which would beacceptable for maintaining the food container 48 within the heatedcontainer 16 at a desired temperature upon delivery to a customer. TheType 45 ink allows the opaque color to appear on the substrate 80 whenthe temperature is at or below 104 degrees Fahrenheit and permits theopaque color to completely disappear to fully reveal the words “It'sHOT” when the temperature is at or above 122 degrees Fahrenheit. Betweenthe two temperatures, there is a gradual change from the opaque color tothe clear color. Moreover, once the temperature of the Type 45 ink is ator above 122 degrees Fahrenheit, it continues to display clearly thewords “It's HOT” for a period of about four to five minutes after thefood container 48 has been removed from the heated container 16 and theseal 78 is exposed to a room temperature of approximately 72 to 75degrees Fahrenheit.

It will be noted that other inks, such as Type 47 or Type 60, areavailable from Prom Edge that may be substituted for the Type 45 ink ifit is desired to have the heat sensitive coating 86 change from anopaque color to a clear color at higher temperature ranges. The Type 47is opaque at or below 111.2 degrees Fahrenheit and is completely clearat or above 136.4 degrees Fahrenheit while the Type 60 ink is opaque ator below 127.4 degrees Fahrenheit and is completely clear at or above149 degrees Fahrenheit. In addition, a thermochromic composition forproviding a color change of the type experienced by the inks referred toabove can be found discussed in the U.S. Pat. No. 4,717,710 entitled“Thermochromic Composition,” issued on Jan. 5, 1988 in the name ofShimizu et al.

The adhesive 82 that has been found to provide excellent adhesion withthe cardboard of the food container 48 can also be obtained from PromoEdge and is made by Spinnaker Coating, Inc. of Troy, Mich. 45373 and isidentified as Spinnaker Coating BP-52. The adhesive 82 is an aggressive,acrylic general purpose permanent pressure sensitive adhesive whichoffers excellent bond permanency to cardboard and a wide variety ofpackaging materials. Accordingly, once placed on the food container 48,the seal 78 cannot be removed without leaving evidence that it has beenremoved. Thus, if someone should try to tamper with the food productwithin the food container 48, it will be evident by the condition of theseal 78.

In practicing the present invention and using the pizza 74 as an exampleof a food product, the pizza 74 is initially baked and removed from theoven and placed on a cutting board. While on the cutting board, thepizza 74 is at a temperature of approximately 200 degrees Fahrenheit.The pizza 74 is then pre-cut into pie-shaped pieces and immediatelyplaced within the food container 48 as seen in FIG. 3 after which thelid 52 is closed. Once the lid 52 is closed, some of the heat from thehot pizza will be transferred to the air within the chamber 76 and aswell as to the food container 48 in its entirety by a combination ofconvection and conduction. At this point the seal 78 is applied to thefront end of the food container 48, as seen in FIG. 4, with theperforations 84 thereof being aligned along the intersection of thefront wall 54 and the plane of the top section and thereby provide atear line for opening the lid 52. When so positioned, the circular heatsensitive coating 86 is located in a conspicuous place on the outersurface of the top section 62 of the lid 52 approximately one and onehalf to two inches from the intersection of the front wall 54 and theplane of the top section 62. At this stage, if the top section 62 of thelid at the location of the heat sensitive coating 86 has being heated toa temperature of 122 degrees Fahrenheit or higher, the heat sensitivecoating 86 will be completely clear to expose the words “It's HOT”. Itwill be noted that during the time that the pizza was prepared andplaced into the food container 48, the lead wire 20 of the heatedcontainer 16 has been plugged into a HOTBAG Power Distribution Unit(PDU) (not shown in the accompanying drawing). The PDU supplieselectrical energy to the resistance wires of the panels 32 and 33 toprovide a temperature in the range of 160 degrees Fahrenheit to 175degrees Fahrenheit within the cavity 40 of the heated container 16. ThePDU and a rack for holding six heated containers 16 is available as anin-store holding system from Check Corporation, 1394 Piedmont, Troy,Mich. 48083. The Check Corporation identifies such system as a 6-PACKPizza Delivery System which includes the rack and incorporates the PDUand six output cables which connect with the connector 22 of the sixheated containers 16 for keeping twelve pizzas hot and ready for pick upor delivery.

After applying the seal 78 to the food container 48, the flap 42 of theheated container 16 is opened and the food container 48 is placed intothe cavity 40 after which the flap 42 is resealed by having the Velcrostrips 44 and 46 reconnected. The food container 48 may be the firstcontainer placed into the cavity 40 or the cavity 40 may already havewithin it another food container 48 as seen in FIG. 2. If the latter isthe case and as seen in FIG. 2, inasmuch as the temperature within thecavity 40 is being maintained in the aforementioned range of 160 degreesFahrenheit and 175 degrees Fahrenheit, the other food container 48 willbe sufficiently elevated in temperature so that the heat sensitivecoating 86 thereon will be clear to expose the words “It's HOT. Also,when the second food container 48 is placed into the cavity 40, the basesection 53 of the second food container 48 will rest upon and cover theheat sensitive coating 86 of the seal 78 on the first food container 48and, through conduction, also serve to transfer heat from its basesection 53 to the heat sensitive coating 86 of the first-to-enter foodcontainer 48 within the cavity 40.

Afterwards, the food containers 48 within the heated container 16 thathave to be delivery to the door of a customer will be removed from thesupport rack by the vehicle operator 12 who will also disconnect thequick release connector 22 from the PDU. The heated container 16 willthen be placed into delivery vehicle, and the connector 22 will beconnected to the power cord 26 and the plug 28 plugged into thecigarette lighter 30 as seen in FIG. 1. By so doing, the temperaturewithin the cavity 40 of the heated container 16 will be continuouslymaintained at the desired temperature which will be evidenced by theheat sensitive coating being clear and revealing the words “It's HOT”.When the vehicle operator 12 arrives at his destination, one or both ofthe food containers 48 will be removed from the cavity 40 of the heatedcontainer 16 and handed to the customer. The customer can immediatelyobserve visually that the words “It's HOT” appearing on the seal 78.This will verify that the food container 48 and the pizza werecontinuously maintained at a desired temperature from the time that thepizza 74 was placed in the food container 48 until it reached thecustomer's door. In addition, inasmuch as the seal 78 serves to join thebody portion 50 of the food container 48 to the lid 62 thereof andcannot be removed without it be evident that it has been removed, thecustomer can rest assured that the pizza was not tampered with from thetime it was placed into the food container 48 up until the customerreceived it.

A modified form of the seal 78 is shown in FIG. 9 and is identified bythe reference numeral 90. It will be understood that the parts of seal90 that are identical to the parts of the seal 78 are identified by thesame reference numerals but primed.

The only difference between the seal 78 and the seal 90 is in the formof the perforations provided in the body of the substrate 80′ so as toprovide a tear line along the intersection of the front wall 54 with thetop section 62 of the food container 48 as seen in FIG. 4 and also tofacilitate the removal of the seal. In this case, rather than having aseries of short aligned perforations 84 as seen in FIG. 5, the substrate80′ has a pair of aligned closely spaced perforations 92 in the form ofstraight elongated slits which would be located in alignment with theaforementioned intersection of the food container 48. In addition, twopair of outwardly radiating aligned perforations 94 and 96, each in theform of an elongated slit, are provided in the substrate 80′ to furtherfacilitate the removal of the seal 90 from the food container 48 by thecustomer in order to free the lid 62 from the body portion 50 of thefood container 48 and gain access to the pizza. It has been found thatby having the perforations 92-96 formed in the substrate 80′ of the seal90 and, as seen in FIG. 9, radiating from substantially the center ofthe substrate 80′, such removal can be readily accomplished by thecustomer.

FIGS. 10 and 11 show a further modified version of the seal 78 that isidentified by the reference numeral 98. As in the case of the seal 90,parts of seal 98 that are identical to the parts of the seal 78 areidentified by the same reference numerals but double primed.

Seal 98 differs from seal 78 and seal 90 in that the substrate 80″ doesnot have any perforations but, instead, is provided with a narrowweakened section 100 which extends along a straight line from one sideedge to the other side edge of the seal 98 as seen in FIG. 10. In otherwords, the thickness of the substrate 80″ is reduced along the section100 to facilitate the tearing of the seal 98 into two pieces. As in thecase of the seals 78 and 90, the weakened section 100 is intended to bealigned along the above-mentioned intersection of the food container 48and serve as a tear line in the manner of the above-describedperforations formed in the seals 78 and 90.

Various changes and modifications can be made to the improved heatedfood container and the method described above without departing from thespirit of the invention. For example, the seal 78 can be made so thatthe words “It's HOT” covered by the heat sensitive coating 86 arelocated closer to the center of the top section of the food container 48while still maintaining the tear perforations 84 at the aforementionedintersection of the lid 52 with the body portion 50. Also, the shape ofthe seal 78 need not be rectangular as shown but could take on otherforms such as being square, triangular or circular. In addition, thetemperature range indicated above for the heat sensitive coating 86 maybe varied the important consideration being that the food product isdelivered to the customer at a temperature of 140 degrees Fahrenheit orhigher. As to the perforations formed in the substrate of the seals 78and 90, although each of the perforations take the form of either shortor elongated straight lines, the perforations can take other forms suchas small circular, elongated or other shaped openings which are closelyspaced to provide tear lines within the substrate. Moreover, the indicia“It's HOT” can be varied so long as the change from the opaque color tothe clear color indicates to the customer that the contents of the foodcontainer 48 are at the desired temperature when delivered to his/herdoor. Such and other changes and modifications are contemplated by theinventor and he does not wish to be limited except by the scope of theappended claims.

What is claimed is:
 1. A seal for a food container having a body portionsupporting a heated food product and said seal serving to visuallyindicate to a customer that said food container has been maintained in aheated condition, said food container adapted to be maintained in saidheated condition by a heating device which provides heat within a firsttemperature range, said body portion having a lid hinged thereto that isadapted to be moved to a closed position to form a closed chamber forsaid heated food product, said seal including a substrate having apressure sensitive adhesive on one side thereof and an indicia on theother side thereof that is covered by a heat sensitive coating and thatvisually indicates said heated condition, said heat sensitive coatingbeing an opaque color so as to conceal said indicia when said heatsensitive coating is at or below the lowest temperature of a secondtemperature range, said heat sensitive coating being completely clear tovisually expose said indicia when said heat sensitive coating is at orabove the highest temperature of said second temperature range, saidsubstrate of said seal adapted to connect said lid to said body portionthrough said adhesive when said lid is in said closed position, and saidsubstrate of said seal having a plurality of closely alignedperforations formed therein, each of said perforations taking the formof an elongated slit adapted to be located at the intersection of saidlid and said body portion when said lid is in said closed position andserves to provide a tear line so as to facilitate the opening of saidlid.
 2. A sealed food container having a body portion supporting aheated food product that is maintained by a heating device at a desiredtemperature within a first temperature range for delivery to a customerin a visually verifiable heated state, a lid hinged to said body portionand adapted to be moved to a closed position to form a closed chamberfor said food product, a seal including a substrate having a pressuresensitive adhesive on one side thereof and an indicia on the other sidethereof that indicates said heated state and is covered by a heatsensitive coating, said heat sensitive coating having an opaque color soas to conceal said indicia when said heat sensitive coating is at orbelow the lowest temperature of a second temperature range, said heatsensitive coating being a clear color to visually expose said indiciawhen said heat sensitive coating is at or above the highest temperatureof said second temperature range, said substrate of said seal connectingsaid lid to said body portion through said adhesive when said lid is insaid closed position so that said indicia is located in a conspicuousplace on said food container and thereby is readily visible when saidfood container is delivered to said customer, said substrate of saidseal having at least one tear line formed therein that is adapted to belocated at the front of said food container at the intersection of saidlid and said body portion when said lid is in said closed position tofacilitate the opening of the lid, the arrangement being such that thelowest temperature of said first temperature range is at a higher levelthan the highest temperature of said second temperature range wherebysufficient heat is provided by said heating device to cause said heatsensitive coating to be in a clear state and expose said indicia whilesaid food container is maintained at said desired temperature by saidheating device and for a predetermined time period after said foodcontainer is no longer heated by said heating device.
 3. The sealed foodcontainer set forth in claim 2, wherein said tear line takes the form ofa pair of perforations each in the form of an elongated slit.
 4. Thesealed food container set forth in claim 2, wherein said more than onetear line radiate outwardly from substantially the center of saidsubstrate.
 5. The sealed food container set forth in claim 2, whereinsaid tear line is formed by having a weakened section in said substrate.6. The sealed food container set forth in claim 4, wherein each of saidtear lines includes a pair of perforations each of which is in the formof an elongated slit.
 7. In combination, a portable heated containerhaving a cavity adapted to be closed by a closure member and to betransported by a motor vehicle from one location to another, an electricreceptacle in said motor vehicle, a heating device incorporated in saidheated container for heating said cavity to a temperature within a firsttemperature range, a food container adapted to be located within saidcavity and to be maintained by said heating device in a heated state,said food container having a body portion for supporting a heated foodproduct, a lid hinged to said body portion and adapted to be moved to aclosed position to form a closed chamber for said food product, a sealhaving a substrate provided with a pressure sensitive adhesive on oneside thereof and an indicia on the other side thereof that is covered bya heat sensitive coating and that indicates said heated state, said heatsensitive coating having an opaque color so as to conceal said indiciawhen at the lowest temperature of a second temperature range and tochange to a clear color to visually expose said indicia when said heatsensitive coating is at or above the highest temperature of said secondtemperature range, said substrate of said seal fixedly connecting saidlid to said body portion through said adhesive and having said indicialocated in a conspicuous place on said food container so as to have saidindicia readily visible when said food container is removed from saidcavity, said substrate having perforations in the form of a pair ofaligned elongated slits adapted to be located at the intersection ofsaid lid with said body portion so as to facilitate the opening of saidlid, and said electric heater having a plug adapted to be connected tosaid receptacle in said motor vehicle to heat and maintain said cavityat a temperature within said first temperature range, the arrangementbeing such that the lowest temperature of said first temperature rangeis at a higher level than the highest temperature of said secondtemperature range whereby sufficient heat is provided in said cavity bysaid heating device to cause said heat sensitive coating to be in aclear state and expose said indicia while said food container is in saidheated container and for a predetermined time period after said foodcontainer is removed from said heated container.
 8. The combination setforth in claim 7, wherein said substrate including a plurality ofadditional perforations radiating outwardly from substantially thecenter of said seal.
 9. The combination set forth in claim 6, whereinsaid heated container includes top and bottom panels each of which hassaid electric heat element incorporated therein for providing saidheating device.
 10. The combination set forth in claim 8, wherein saidadditional perforations consist of pairs of aligned elongated slitsradiating outwardly from substantially the center of said seal.